1. Field of the Invention
This invention relates to a multi-media communication system using an Integrated Service Digital Network (ISDN), and more particularly to an ISDN-based video conversation/monitoring system applicable to a complex conversation service system that includes a remote monitoring function.
2. Description of the Related Art
Conventional guidance systems, conversation systems and monitoring systems which communicate images, sounds and data, as well as complex systems that integrate these types of systems, use analog telephone lines, dedicated communication lines, or optical fiber lines or the like. An example of such systems is described in Japanese patent publication JP-A-4-21095 and JP-A-4-315351.
The above-mentioned prior art systems, when an existing analog telephone line is used, has problems in that the transmission line has a limited band width, which consequently makes it difficult to transmit efficiently moving image signals and complex signals that carry sound, images, and control data. Furthermore, such prior art systems typically employ a center station and end station facilities which are of large scale and which necessitate a large installation space.
The above-mentioned prior art systems, when a dedicated line or optical fiber line is used, has problems in that a new transmission line needs to be constructed, the service range and scale are limited by the network construction, all of which make construction of the system very expensive.
The above-mentioned prior art systems, when a public integrated-service digital communication network is used for the communication line, which advantageously removes the need for construction of a new communication line significantly reduces the operating communication cost of the system, has a particular problem in that the system is accessible by unlicensed terminal stations through the public communication line and the handling of information will be intricate for secrecy protection.